1. Field of the invention
The present invention relates to an apparatus to facilitate the coating of a running layer of material, in particular paper and/or cardboard. The invention also relates to a method of establishing the desired cross-sectional profile of the liquid or pasty coating medium across the width of a moving layer of material.
2. Description of the related art
It is known to integrate devices into so-called coating machines (and applicator implements) for applying one or several layers of liquid or pasty coating media onto one or both sides of a moving layer of material, such as paper, cardboard, or textile fabrics. Typically, coating media include, for example, coatings containing pigments, starches, or liquids used to impregnate a material and so forth.
According to the direct application method, an applicator device applies the coating medium directly onto the moving layer of material along a segment where the material layer is supported by a moving surface, such as for example, a counter roller or a continuous conveyor belt. For this sort of approach, the applicator implement also often functions as a pre-regulator (also pre-metering) device that dispenses predetermined amounts of the liquid or pasty coating medium, which in these cases are intentionally in excess of what is required. After the moving layer of material has passed the pre-regulating/dispenser device, it passes a second regulator device, also known as a fine-metering device, fine-dosing device, or leveling device. The second regulator device readjusts the previously dispensed amounts of liquid or pasty coating medium, and can include a spreader element, a coating blade, a spreader roller, or a rolling wiper stick. The second regulator device generally extends across the entire width of the moving layer of material, and is pressed onto the surface of the material layer. Further, the second regulator device wipes the excess amounts of liquid or pasty coating medium off of the moving material layer, and thus leaves the desired quantity of coating medium on the surface of the moving material layer. The second regulating or fine-metering device is usually subdivided into a large number of segments which extend along the width of the moving material layer. Each segment is associated with an actuator which can be independently controlled. Thus, the profile shape and the pressure of the blade or wiper along each segment onto the material layer can be defined separately, so that ultimately the desired cross-sectional profile of coating medium can be achieved. The actuators are usually remotely controlled by an automatic control system which gathers measurements of the thickness of the applied coating of liquid or pasty medium. The actuators can also be adjusted by hand.
More recent applicator implements already contain pre-regulating dispenser devices with adjustable cross-sectional profiles that can control the thickness profile of the applied coating. For this purpose, one uses a pre-regulating dispenser device with a free streaming jet applicator implement whose exit nozzle is formed by two lips, i.e., one lip upstream and one lip downstream relative to the passage of the moving material layer. The two lips are also sub-divided into segments along the width of the moving layer of material, where an actuator is associated with each of the segments in the up-stream and the down-stream lip. With the actuators, either lip can be either adjusted as a whole or the distances between the consecutive segments of each lip can be adjusted individually. It is also possible to adjust both lips simultaneously. The before-mentioned actuators are either remotely controlled or can be adjusted manually, whereby the automatic control of the individual actuators is set up as a closed loop system which adjusts the actuators based on input received concerning the thickness profile of the applied coating of liquid or pasty medium. Such an applicator implement has been mentioned in the German Document No. 4432177 and is known under the trademark "Jet Flow F".
The combination of pre-regulating and finishing regulating devices can be distinguished in two different categories, i.e., one where the pre-regulating and the finishing regulating are spatially separated in two different compartments and another where the two operations take place right next to one another, without spatial separation. The spatially separated version is such that the first metering device is associated with a first counter roller while further down along the path of the moving layer of material a second metering device is associated with another counter roller. Such a configuration of an applicator implement is already known from the German Document No. 3715307. A connected version of pre-metering and finishing metering devices, on the other hand, is such that both devices are associated with the same counter roller.
Another applicator implement for a similar procedure to regulate the profile of the coating thickness of a liquid or pasty medium across the width of a moving layer of material, in particular paper or cardboard, can be found in an appended note with the official symbol 196 05 183.5 which is characterized by the use of actuators to control the coating thickness at a pre-regulating device as well as a finishing regulating device. The combination of both adjustments results in the desired overall correction of the profile of the coating thickness.
This solution produces a coating thickness that requires only very little readjusting to the cross-sectional profile across the material layer width in the second metering step. Thus, the finishing regulating device, especially if it is a spreader blade, will be spared from premature uneven wear and will have a much longer service life.
Since this method relies on very minute synchronized movements of a number of actuators in order to obtain the desired adjustments to the coating thickness, the construction of the device requires a considerable amount of precision and regard to detail.